Abstract: Various embodiments of the present disclosure are directed towards free-piston combustion engines. As described herein, a method and system are provided for displacing a free-piston assembly to achieve a desired engine performance by repeatedly determining position-force trajectories over the course of a propagation path and effecting the displacement of the free-piston assembly based, at least in part, on the position-force trajectory. In a dual-piston assembly free-piston engine, synchronization of the two piston assemblies is provided.

Abstract: An example social media messaging system may include a capability for a user to edit messages after the messages have been posted to the messaging system. The capability is implemented in a manner that preserves the immutability of messages that are posted to the messaging system.

Abstract: A method for purchasing processing requests on a messaging platform including obtaining a broadcast message from a first client associated with a first social networking account, making a first determination that the broadcast message includes a reference to an item, making a second determination, based at least in part of a perceived inventory count for item that a vendor associated with the messaging platform is able to supply the item, based on the second determination, generating a new broadcast message that includes a buy-now card associated with the item, transmitting the new broadcast message to a second client associated with a second social networking account, receiving, after transmitting the new broadcast message, a purchase request for the second client, wherein the purchase request specifies the item, and processing, by the messaging platform, the purchase request.